Through Mold Via (TMV) is a technology used with integrated circuit Package-on-Package (POP) Integrated Circuit (IC) connections. A first chip package has solder bumps on the bottom for reflow-soldering, for example, to a printed circuit board. The first chip package also has pads or solder pumps exposed on its top surface for the purpose of enabling a second-chip package to be positioned on the top of the first-chip package and reflow soldered thereon in order to establish electrical connections between solder bumps on the bottom of the second-chip package and the solder bumps or pads on the top of the first-chip package.
During the manufacturing process of a TMV POP assembly, a top IC package, having solder locations on its bottom surface, is soldered to the top of a bottom IC package having solder pads and/or solder balls on its top surface. During the solder reflow process the top package is positioned on top of the bottom package and aligned with the appropriate solder connections. As the solder reflow process progresses, the temperature is increased until the solder flows and the top IC package “collapses” (closes the gap originally created by the solder balls between the two packages) down onto the bottom IC package. In other words, as the solder bumps between the top IC package and the bottom IC package melt, the top IC package lowers onto or becomes much closer to the top of the bottom IC package thereby significantly decreasing any gap distance that existed between the two packages prior to the reflow process.
In general, all Ball Grid Array (BGA) packages that have solder balls on their bottom surface collapse or significantly close the gap between the bottom surface of the BGA package and the top surface to which the BGA package is being soldered during the reflow or substantially similar soldering process.
For example, if the standoff height (i.e., the gap between the bottom of a BGA package and a PC board) is about 12 mils, then when the solder reflow process occurs and the solder balls on the bottom surface of the BGA package melt, the standoff height or gap may decrease to less than about 8 mils between the bottom surface of the BGA package and the top of the PC board. Thus, the BGA package collapses or moves down about 4 mils or more when the solder balls are reflowed to form the electrical connections and solder joints therebetween. In some situations the package collapses to less than 1 mil or collapses in an un-uniform manner such that the top package is slanted or tilted.